For the home gardener and caneberries, there is no need to limit initial fruit production.
Most home gardeners would want to sample the fruit as soon as possible.
If last year’s canes are more than waist high, they may surprise you. If you get very few or no blooms, cut them down then, unless they put out a lot of leaves (helps feed the roots).
If there are no green leaves remaining, then cutting them down now will not significantly affect this year’s new canes.
They’re both floricane bearing berries, so last year’s canes will fruit this year. If you cut those down, then this year’s canes won’t fruit until next year. There’s no reason to cut them down this year, and they shouldn’t have any bearing on this year’s new canes. How tall are they?
12" will not contribute anything except as markers to avoid stepping on or cultivating too closely. I would leave them in as markers until new growth is obvious.